An electronic engine control system has been widely used as a control system to control a fuel injection unit to supply fuel to an internal combustion engine using an injector (an electromagnetic fuel injection valve) or an ignition unit to ignite the engine.
The electronic engine control system comprises a controller having an ignition control section to control the ignition unit, a fuel injection control section to control the fuel injection unit, both of which are formed of a microprocessor and an electric supply source section to apply a driving power to the ignition unit, the fuel injection unit and the controller.
Of late, there have been used such an electronic engine control system for a vehicle engine of relatively small exhaust amount started by a starter such as a kicking starter or a recoil starter to be operated by a human power without any battery mounted thereon or a general-purpose engine.
In the vehicle having no battery mounted thereon, there is provided an electric power source section formed of an AC generator driven by the engine and a converter to convert an output voltage of the generator into a DC voltage to supply the driving power from the electric power source section to the ignition unit, the fuel injection unit and the controller.
The ignition control section comprises an ignition timing arithmetical operation part to arithmetically operate an ignition timing on control conditions such as a rotational speed and others and an ignition command generation part to generate an ignition command to be applied to the ignition unit when the ignition timing is detected by making a counting operation for detecting the arithmetically operated ignition timing by means of an ignition timer.
The fuel injection control section comprises: an injection amount decision section to decide a fundamental injection amount of fuel necessary for obtaining a mixture gas of predetermined air-to-fuel ratio for an intake air amount detected based on a throttle opening degree α of the engine (an opening degree of a throttle valve) and a rotational speed N thereof and to correct the fundamental injection amount of fuel in accordance with various control conditions such as an atmospheric pressure, an intake air temperature, a temperature of cooling water of the engine etc. to decide an actual injection amount; an injection command generation section to generate an injection command at predetermined injection timing; and an injector drive part to drive an injector in accordance with the injection command to make an injection of fuel. The amount of fuel injected from the injector is decided on a time during which the fuel is injected (an injection time) and a pressure of fuel which is applied from the fuel pump to the injector. In general, with the constant fuel pressure applied to the injector, the injector is driven for the injection time arithmetically operated for the fuel injection amount whereby the predetermined amount of fuel is injected from the injector.
In order to control the ignition timing and the injection amount of fuel of the engine, it is required to provide information of a crank angle and of a rotational speed of the engine to the controller. To this end, in the case where the ignition timing and the fuel injection amount of the engine are controlled by the electronic engine control system, there has been mounted on the engine a signal generation device to generate a pulse signal at a predetermined crank angle position of the engine whereby the crank angle information is obtained from each pulse signal generated by the signal generation device, and the rotational speed information of the engine is obtained from a generation interval of the pulses generated at the specific crank angle position by the signal generation device (or the time required for one revolution of a crankshaft of the engine).
There has been used as the signal generation device a pulser to generate first and second pulses having different polarities when there are detected a front edge and a rear edge of a rotational direction of a reluctor formed of a protrusion or a recess provided on or in an outer periphery of a flywheel of a flywheel magnet rotor mounted on the crankshaft of the engine.
The signal generation device may be so formed that the front edge of the reluctor is detected, at a timing suitable for a timing when a measurement of the ignition timing determined by the arithmetical operation starts and also suitable for a timing when the sequential injection of fuel is made, to generate a front edge pulse signal and that the rear edge of the reluctor is detected, at a timing suitable for the ignition timing when the engine starts and rotates at a low speed, to generate a rear edge detection pulse.
In the case where such a signal generation device is used, the ignition control section serves to make an ignition operation when the pulser detects the rear edge of the reluctor at starting the engine to generate the rear edge pulse, and also serves to make the ignition operation when the measurement of the ignition timing is completed, the measurement being started when the pulse generates the front edge pulse after the engine starts in a range where the rotational speed exceeds a set value.
Also, the fuel injection control section serves to drive the injector to make the sequential injection of fuel when the signal generation device generates the front edge detection pulse.
At least one revolution of the crankshaft will be required for obtaining the rotational speed information necessary for the arithmetical operation of the fuel injection amount after the initiation operation of the engine starts in the case where the aforementioned signal generation device is used, and furthermore, the fuel injection of proper amount corresponding to a cranking speed will not be able to be made until the arithmetical operation of the fuel injection amount based on the rotational speed information is completed.
With the battery mounted on the vehicle and so on driven by the engine, the crankshaft can be rotated by the starter motor until a proper amount of the fuel with which the rotational speed is reflected is injected when the engine starts, and therefore there is no trouble for starting the engine. However, in the case where the engine is started by a starter such as a kicking starter or a recoil starter operated by a human power, the crankshaft can be rotated just two or three times by cranking on the starting operation and therefore, the proper amount of fuel with which the rotational speed is reflected cannot be injected as described hereinafter, which deteriorates the startability of the engine.
FIGS. 6A through 6E are time charts to show the starting operation of a four cycle single cylinder engine which has no battery mounted thereon and is started by the kicking starter with the prior control system. FIG. 6A shows the front edge detection pulses Vs1 and the rear edge detection pulses Vs2 output by the pulser relative to time t, and FIG. 6B shows the injection command signals Vj. FIG. 6C shows the ignition command signals Vi, FIGS. 6D and 6E show the output voltage Vcc of the electric power source section having the generator used as the electric power source and the fuel pressure FP applied to the injector, respectively.
In FIG. 6A, “EXP” and “EXH” designate an expansion stroke and an exhaust stroke, respectively, while “INT” and “COM” designate an intake stroke and a compression stroke, respectively.
The electric power source section having the generator used as the electric power source section comprises a converter having a function to rectify the output of the generator and a function to regulate the voltage so that the rectified output never exceeds a regulation value, whereby the DC voltage Vcc, regulated so as not to exceed the regulation value Vr, is output as shown in FIG. 6D. The output of the electric power source section is applied to the fuel pump and the injector and also to a power source terminal of the microprocessor after reduced by a constant voltage electric power source circuit to a constant voltage (5V) suitable for driving the microprocessor. The output voltage Vcc of the electric power source section varies in the same manner as the output voltage of the generator until it reaches the regulation value Vr (about 16V in the illustrated embodiment) of the output voltage of the electric power source section. Thus, the variation in the output voltage Vcc of the electric power source section on the start of the engine can be regarded as that in the output voltage of the generator.
There appear depressions in a waveform of the output voltage Vcc of the electric power source section whenever the injection command signal or the ignition command signal is generated in the process in which the output voltage of the generator rises towards the regulation value Vr at the time of starting of the engine. In FIG. 6D, the depression a appearing in the waveform of the output voltage Vcc of the electric power source section corresponds to that of the electric power source voltage produced by the generation of the injection command Vj1, while the depression b of the same waveform corresponds to that of the electric power source voltage produced by the generation of the injection command Vj2. The depressions c and d in the waveform of the output voltage Vcc correspond to those of the electric power source voltage produced by the generation of the ignition command signal Vi1 and the injection command Vj3, respectively. The depression e corresponds to that of the electric power source voltage produced by the generation of the ignition command signal Vi2.
In the example shown in FIG. 6, after the starting operation begins and when the output voltage Vcc of the electric power source section reaches an initiation voltage Vo (5V, for instance) of the microprocessor, this microprocessor is initiated at time t1. Then, when the pulser generates the front edge detection pulse Vs1 at time t2, the injection command Vj2 is generated. The signal width of the injection command signal is determined on the sum of the injection time to determine the injection amount and a useless injection time (a time until it starts the injection of the fuel after the drive voltage is applied to the injector).
In FIG. 6, the injection command Vj1 is generated when the microprocessor is initiated at time t1, which will be described later. Herein, it is supposed that the injection command Vj1 is not generated.
Although the fuel injection time at time t2 may be determined by the arithmetical operation, the microprocessor, which the controller is formed of, arithmetically operates the fuel injection time using the rotational speed set when it is initialized because no practical rotational speed information is yet detected at time t2.
The injection command generated at time t2 is applied to an injector drive circuit. Thus, the injector drive circuit applies a drive voltage to the injector, but the output voltage of the generator still does not reach a valve openable voltage V1 at time t2, and the output voltage Vcc of the electric power source section also does not reach the valve openable voltage. Therefore, the injector cannot inject the fuel of injection amount arithmetically operated.
In general, when the engine stops, the piston cannot exceed a top dead center in the course of the compression stroke. Thus, in most cases, when the engine should start, the compression stroke and the expansion stroke are performed by the first revolution of the crankshaft, and the exhaust stroke and the intake stroke are performed by the second revolution. In the example of FIG. 6, the expansion stroke begins at time t3.
Accordingly, when the injection command Vj2 is generated at time t2, the engine is in the compression stroke (COM), and an intake valve is closed so that the injected fuel is never inhaled into the cylinder.
When the signal generation device generates the rear edge detection pulse Vs2 at time t3, the ignition command signal Vi1 is applied to the ignition circuit so that the ignition operation is performed, but since the fuel is not yet inhaled into the cylinder, the first explosion of the engine cannot occur.
At time t4, the output voltage of the generator reaches the valve openable voltage V1 that enables the injector to open the valve, at time t4 and the output voltage Vcc of the electric power source section also reaches the valve openable voltage, but since the time t4 is not the sequential injection timing, the injection command is never generated and no injection of fuel is performed even though the output voltage Vcc of the electric power source section reaches the valve openable voltage.
Since the pulser again generates the front edge detection pulse at time t5, the rotational speed is renewed. Since the injection command Vj3 is generated at time t5, the injector injects the fuel. The injection time at that time is already arithmetically operated before time t5. Thus, it will be noted that the injection at time t5 does not yet reflect the actual rotational speed, and therefore the injection of fuel with the amount suitable for the conditions of the engine is not performed.
When the pulser generates the rear edge detection pulse at time t6, the ignition operation is performed, but since this timing is one at which the exhaust stroke (EXH) terminates, no combustion occurs.
When the intake stroke begins at time t6, the fuel injected and evaporated into the intake pipe at time t2 and the fuel injected and evaporated into the intake pipe at time t5 are inhaled into the cylinder.
The fuel is injected on the injection command Vj4 at time t7 with the amount reflecting the rotational speed of the engine, but since the engine is in the compression stroke at time t7, the fuel injected on the injection command Vj4 is not yet inhaled into the cylinder.
When the pulser generates the rear edge detection pulse at time t8, the ignition operation is performed. As this ignites the mixture gases, the first explosion occurs and the engine starts.
In order to positively start the engine at time t8, the proper amount of fuel (the mixture gas of proper air-to-fuel ratio) should be inhaled in the intake stroke from time t6. The fuel to be inhaled into the cylinder in the intake stroke from time t6 is the one injected when the injection command Vj2 is generated at time t2 and the one injected when the injection command Vj3 is generated at time t5. However, the amount of fuel able to be injected when the injection command Vj2 is generated at time t2 tends to vary widely on the voltage Vcc and the fuel pressure FP at time 22. Even though the signal width of the injection command Vj3 is set at a proper value, there are some cases where the amount of fuel inhaled into the cylinder becomes improper according to the amount of fuel injected when the injection command Vj2 is generated. In addition thereto, since the signal width of the injection command Vj3 is the improper value, which does not reflect the rotational speed, in some cases, the fuel in the cylinder becomes insufficient or excessive at time t8 when the first explosion should be made and this prevents the positive ignition and deteriorates the startability of the engine.
As aforementioned, in order to positively start the engine at time t8, it is required that the fuel injection should be made so as to be able to inhale the fuel of proper amount, which reflects the rotational speed in the intake stroke from time t6. However, in the case where the engine is started by the starter such as the kicking starter or the recoil starter operated by the human power, the crankshaft can be rotated only two or three revolutions by cracking and therefore it is hard to inject the fuel of proper amount, which reflects the actual rotational speed when it should start.
In order to prevent the poor startability of the engine due to insufficient amount of fuel, it has been proposed to prevent the insufficient amount of fuel when the first explosion is performed by the first fuel injection during a predetermined time, which is made by the injection command Vj1 when the microprocessor initiates as described in Japan Patent No. 3086335. In the proposed invention, when the microprocessor initiates at time t1 of FIG. 6, the first predetermined injection time is set on the temperature of the cooling water of the engine so that there is generated the drive command Vj1 having the signal width corresponding to this predetermined injection time whereby the fuel injection is performed.
However, if the vehicle having no battery mounted thereon makes the first fuel injection on the initiation of the microprocessor, there occur the following problems.
Even if the injection command Vj1 is generated so as to inject the fuel during the predetermined time set in accordance with the temperature of the cooling water when the microprocessor is initiated at time t1 of FIG. 6, the voltage of the generator does not yet reach the valve openable voltage V1 (which is generally higher than the voltage necessary for initiating the microprocessor), and therefore the valve of the injector almost cannot be opened even if the injection command Vj1 is generated. Also, since the fuel pressure FP applied by the fuel pump is relatively lower, the fuel almost cannot be injected practically.
Because of the unstable useless injection time of the injector at times t1 and t2 when the output voltage of the generator does not reach the valve openable voltage, even if the valve of the injector could be opened, the fuel of the amount as determined by the arithmetical operation cannot be injected.
Although the output voltage of the generator exceeds the valve openable voltage V1 at time t5, the injection at time t5 reflects no actual rotational speed of the engine.
Although the fuel injection at time t7 reflects the actual rotational speed of the engine, the fuel injected at time t7 cannot be inhaled into the cylinder because the engine is in the compression stroke at time t7. Thus, the fuel injection at time t7 has the air-to-fuel ratio never reflected at time t8. In order to positively make the first explosion with the proper value of the air-to-fuel ratio of the mixture gas in the cylinder at the ignition at time t8, the fuel should be injected with the proper value reflecting the conditions of the engine before time t6 when the intake stroke begins.
On the start of the engine, the intake air amount varies due to the cranking speed. With the opening degree of the throttle kept constant, the higher the cranking speed is, the less the intake air amount is, and the lower the cranking speed is, the more the intake air amount is. However, in the prior fuel injection control, since the cranking speed is not considered when the injection time of the first fuel injection at the start is determined, the cranking speed becomes lower due to shortage of the operative force on the initiation operation and therefore the injection amount of the fuel is shorted when the intake air amount increases so that the air-to-fuel ratio becomes leaner whereby the startability of the engine is deteriorated.
Furthermore, since, in the prior control system, the ignition operation is made at time t3, which is the state where the enough amount of the fuel is not still injected, excessive electric power is consumed at the start, which disadvantageously causes the output voltage of the generator to become late to reach the valve openable voltage V1.